1. Field of the Invention
This invention relates to cameras and, more particularly, to an automatic focus adjusting device in camera systems.
2. Description of the Related Art
The AF system for a video camera has its AF sensitivity and capability of moving the lens determined in adaptation to the various characteristics (for example, focal length, F-number at full open aperture and position sensitivity) of the lens system that camera carries therein. Also, the actuators for driving the lens and the diaphragm (including an electric motor for driving the lens group for focusing) and the encoders for detecting the operating positions of these members are connected, in the general case, directly to the AF control circuit. It is the present state of art that the design of the AF control circuit has to change individually by every lens type.
However, the above-described conventional example, when applied to the AF controlling of, for example, the lens-interchangeable camera system, because the versatility of the system itself is so low as not to accommodate all differences of each of the lens characteristics from type to type, produces problems such as those shown below.
(1) The AF control hardly suits with the changes of those many factors which are characteristic of the lens, such as the focal length, F-number and position sensitivity, as the lens is interchanged. Concretely speaking, the action up to the sharpest focus will be extremely slow, hunting will be caused not to stop when the in-focus state nears, or other faulty operations will take place with a high possibility.
(2) A lens system capable of matching with different AF models is difficult to design.
(3) Under the circumstances, in order to enhance the repertory of usable lenses, a large scale of memory elements must be used to process information when AF is in operation. This leads to a limit on improvement of the versatility, thus giving a main cause of hindering the camera system from a capability of using interchangeable lenses.